How it works: Ocular axial length measurement

Determination of the effective optical length of the eye is of key importance for selection of suitable lens implant following cataract extraction and to those involved in myopia management.

The more significant contribution of approximately 2/3 of the eye’s refractive power of the air/cornea boundary is determined by keratometry where measurements are principally made of the curvature of the anterior cornea.

IOL power calculations are significantly affected by errors in determined values of axial length of the eye and where an error of 1mm is typically associated with a refractive error of 3.00 D. 

Even as the history of the first 50 years of using ultrasound to investigate the structure of the eye was being celebrated,¹ the use of optical radiation in this role was emerging and has become the dominant technology for use in axial length measurement.